Retreading of tires

ABSTRACT

The invention provides for a method of and means for the retreading of tires. In accordance with the invention a tire is retreaded by enclosing it in a flexible envelope, sealing the envelope, establishing a higher pressure outside the envelope to force the envelope against the new tread and thereby to force the new tread against the tire casing, and raising the ambient temperature outside the envelope.

United States Patent [191 Martin 1 Oct. 30, 1973 RETREADING 0F TIRES[75] Inventor: Aubrey Wilfred Martin, Heilbron,

South Africa [73] Assignee: Republic Rubber Industries (Proprietary)Limited, Heilbron, South Africa [22] Filed: Apr. 26, 1971 [21] Appl.No.: 137,194

[30] Foreign Application Priority Data Dec. 18, 1970 South Africa70/8547 [52] US. Cl. 156/96, 156/394, 156/128, 264/315, 264/326, 425/17,425/43, 425/39, 425/44 [51] Int. Cl B29h 5/04, B29h 17/36 [58] Field ofSearch 156/96, 110, 394, 156/128, 127, 129; 264/315, 326; 425/17,

[56] References Cited UNITED STATES PATENTS 3,325,326 6/1967 Schelkmann156/394 X 3,236,709 2/1966 Carver 156/96 1,579,641 4/1926 2,292,2868/1942 2,966,936 l/196l 2,976,910 3/1961 Nowak 156/96 FOREIGN PATENTS ORAPPLICATIONS 746,375 3/1956 Great Britain 156/96 Primary Examiner-AlfredL. Leavitt Assistant Examiner-C. B. Cosby Att0rneyl(arl W. Flocks [5 7]ABSTRACT The invention "provides for a method of and means for theretreading of tires. In accordance with the invention a tire isretreaded by enclosing it in a flexible envelope, sealing the envelope,establishing a higher pressure outside the envelope to force theenvelope against the new tread andthereby to force the new tread againstthe tire casing, and raising the ambient temperature outside theenvelope.

1 Claim, 3 Drawing Figures RETREADING or TIRES BACKGROUND OF THEINVENTION THIS INVENTION relates to improvements in or relating to theretreading of tires. The invention relates in particular to an improvedmethod of and apparatus for the retreading of tires.

SUMMARY OF THE INVENTION According to the invention there is provided amethod of retreading tires including locating a tread over the treadzone of a tire casing, enclosing the tread and tread zone in a flexibleenvelope, establishing a superatmospheric fluid pressure at ambienttemperature outside the envelope to force the envelope against the treadand the tread against the casing, and raising the ambient temperatureoutside the envelope.

Further according to the invention there is provided apparatus for theretreading of tires by enclosing a tire casing and a tread in a flexibleenvelope, the apparatus including means to establish a super-atmosphericfluid pressure outside the envelope, and means to raise the ambienttemperature outside the envelope.

The means to establish a super-atmospheric pressure may be a pressurevessel. The temperature in the pressure vessel may be raised byintroducing a heated fluid, such as steam, under pressure into thepressure vessel.

The method may include the further step of applying suction to the spacebetween the flexible envelope and the tire casing and sucking out airfrom -this space.

The super-atmospheric fluid pressure may be in the form of a gas such asair under pressure.

The tread may be in strip form and may be pre-cured.

Conveniently, a bonding composition may be provided 1 between the treadand the tire casing-The bonding composition may be a rubber compoundadapted to cure at a temperature in the region of 85C.

The flexible envelope may have a peripheral slit to be positioned alongthe tread region of the tire casing. The envelope may be fitted over thetread and over the tire casing by interfolding the marginal regions ofthe envelope a plurality of times within one another.

The invention is now described by way of an example with reference tothe accompanying drawings, in-

which:

FIG. 1 shows a cross-sectional view of a tire casing and a treadenclosed in a flexible envelope;

FIG. 2 shows diagrammatically a longitudinal sectional view of apressure vessel, tire casings in the pressure vessel and ancillaryapparatus; and

FIG. 3 shows a section on line III-Ill of FIG. 2.

Referring to FIG. 1, reference numeral 10 indicates generally acombination comprising a tire casing 12, a tread 14 and a flexibleenvelope 16. The combination 10 is prepared and assembled as follows.

The tread zone 18 of the tire casing 12 is prepared in a theconventional manner for receiving the new tread 14. The new tread 14,pre-cured and in strip form is prepared in the conventional manner forfitting into the tread zone 18. A bonding composition in the form of arubber compound which will cure at the relatively low temperature of 85C is applied to the tread zone 18. The new tread 14 is affixed to thecompound on the tread zone.

The tire casing 12 with the new tread 14 affixed to it is now enclosedin the flexible envelope 16 which is impervious to fluid flow. Theenvelope which may be of an elastic material such as rubber, isperipherally slit. It is fitted over the tire casing 12 and new tread 14by interfolding the marginal regions 20 a plurality of times within oneanother. A one-way valve 22 is provided in the flexible envelope throughwhich air may be sucked out from the space between the envelope and thetire casing. When air is thus sucked out, the envelope 16 is forcedagainst the tread 14 which is thereby forced against the tire casing 12.

Referring now to FIGS. 2 and 3, there is shown a pressure vessel 24having a hinged door 26 for providing access into the interior of thevessel. Inside the vessel is provided a hanging rail 28 and hooks 30 forsupporting light tires such as passenger vehicle tires. Tracks 32 areprovided at the lower region of the vessel for supporting and guidingcarriages 34. The carriages 34 are adapted to support heavy tires suchas truck and earth moving vehicle tires.

A manifold 36 is provided inside the vessel having branches 38 by meansof which it may be connected 'to the one-way valves in the envelopes 16through flexible tubes 40. The manifold 36 is connected to a suctionpump 42.

A compressor 44 is connected to the pressure vessel 24 via a connection46 and a valve 48 to establish a super atmospheric'air pressure insidethe vessel 24. A boiler 50 is connected to the vessel 24 by means of aconnection 52 and a valve 54 to introduce steam under pressure into thepressure vessel 24. A pressure gauge 56and a temperature guage 58 areprovided for measuring the pressure and temperature of fluid underpressure in the pressure vessel 24. Reference numeral 60 indicates apressure relief safety valve and 62 and 64 indicate a steam trap valveand steam blow down and drain valve respectively.

In operation the combination 10 of tire 12 and tread l4 enclosed inenvelope 16 is placed in the pressure vessel 24..The flexible connection40 on the manifold 36 is connected to the valve'22 in the envelope andthe door 26is closed. The suction pump 42 is operated to suck out airfrom the space between the envelope and the tire casing. Air underpressure is pumped by the compressor 44 into the vessel 24 at ambienttemperature until the pressure in the vessel is about 4.2 kg/sq.cm. (60lbs/sq.inch). Steam is then injected into the pressure vessel from theboiler 50 to heat the compressed air in the vessel to a temperature ofabout C and the pressure in the vessel is raised to about 6.0 kg/sq.cm.(85. lbs/sq.inch)-.

The suction on the envelope is maintained for about 30 minutes aftervessel 24 is pressurized.

The pressure of 6.0 kg/sq.cm. at a temperature of 85 C is maintainedfor: 1% hours for passenger vehicle tires; 2 hours and longer for truckand earth moving vehicle tires.

An advantage of the invention is that by applying fluid (air) pressurefirst at ambient temperature into a pressure vessel before raising thetemperature in the vessel by introducing a heated fluid (steam), thedangers of a premature cure are avoided or at least reduced. Any leaksin the envelope may be detected and rectified before the temperature inthe vessel israised. whereby the defective curing of tires is avoided.

I claim:

1. A method of retreading tires including locating a precured tread ofthe tread zone of a tire casing with an uncured bonding materialinterposed between the casing, after establishing the super-atmosphericpressure outside the envelope, raising the ambient temperature outsidethe envelope to the curing temperature of the bonding material by theinjection of steam, and maintaining the super-atmospheric pressure andthe raised temperature until the bonding material is cured and bonds thetread to the tire casing.

1. A method of retreading tires including locating a precured tread ofthe tread zone of a tire casing with an uncured bonding materialinterposed between the tread and the tire casing, enclosing the treadand the tread zone in a flexible enVelope, rapidly establishing asuper-atmospheric fluid pressure at ambient temperature below curingtemperature outside the envelope thus avoiding precuring of said bondingmaterial, exhausting air from the space between the envelope and thetire casing by applying suction and forcing the envelope against thetread and the tread against the tire casing, after establishing thesuperatmospheric pressure outside the envelope, raising the ambienttemperature outside the envelope to the curing temperature of thebonding material by the injection of steam, and maintaining thesuper-atmospheric pressure and the raised temperature until the bondingmaterial is cured and bonds the tread to the tire casing.